Logging-while-drilling (LWD) systems are used to produce borehole and formation images of several parameters of interest. The logging instrument or “tool” is typically disposed in a collar of the borehole assembly, which is terminated by a drill bit. Data used to generate the images are collected while the LWD logging tool rotates as the drill bit advances the borehole. Images obtained with LWD are obtained from a variety of measurements including natural gamma radiation, bulk density, acoustic properties, and electromagnetic properties such as resistivity. LWD imaging tools typically produce large amounts of data per depth interval of borehole advancement. It is operationally desirable to obtain borehole images in real time at the surface of the earth. Typical LWD telemetry systems include a mud pulse system, electromagnetic telemetry system, or an acoustic telemetry system that uses the drill string as a data conduit. The telemetry rates of these devices range from 1 to 20 bits per second. Because of these slow telemetry rates, imaging data from LWD tools cannot be transmitted to the surface in real time unless the data are significantly compressed.
Several compression methods have been developed over the years to transmit LWD image data in real time. However, these methods use generic and lossy mathematical techniques and typically result in significant loss of data quality.
Once borehole images are obtained, the direction of any dipping beds that intersect the borehole are typically determined by manually correlating centroid tips in the images with absolute measures of azimuthal direction.